The field of the invention is high precision amplifiers for data acquisition systems and, more particularly, high precision composite amplifiers consisting of two integrated circuit operational amplifiers (op amps) connected in cascade.
High precision amplifiers are known in the art. A high precision application, as the term is used herein, is one which requires an accuracy of approximately 0.005%. It is generally known that the precision available from an amplifier is related, among other things, to the open loop gain of the amplifier. In applications where high speed is not required, single stage op amps are commercially available which provide sufficient gain. However, high speed op amps have substantially lower open loop gains, owing to tradeoffs made to achieve high speed performance. A high speed application, as the term is used herein, is an application which requires a settling time of approximately 700 nanoseconds (nS). When an application demands both high precision and high speed, it means that within the required settling time, (700 nS) the output must have settled to within the required precision (0.005%).
Because of the reduced gain of available single stage, high speed op amps, prior high speed, high precision amplifiers often comprised two high speed op amps connected in cascade. In that configuration, the net gain of the composite pair of op amps is the product of their individual gains, which is sufficient for high precision applications. However, in order to stabilize the composite configuration, a compensation network is necessary. Prior compensation networks have worked well in low speed applications, but result in degraded high speed performance, e.g. settling time, of the composite amplifier. Prior configurations of composite op amps have therefore been able to achieve the necessary precision, but have been limited in high speed performance due to delays introduced by the compensation circuits used.